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DOS-based systems make the logical parallel ports detected by the BIOS available under device names such as LPT1, LPT2 or LPT3 (corresponding with logical parallel port 1, 2, and 3, respectively). These names derive from terms like Line Print Terminal , Local Print Terminal (both abbreviated as LPT ), or Line Printer.
An IEEE 1284 36-pin female on a circuit board. In the 1970s, Centronics developed the now-familiar printer parallel port that soon became a de facto standard.Centronics had introduced the first successful low-cost seven-wire print head [citation needed], which used a series of solenoids to pull the individual metal pins to strike a ribbon and the paper.
This places an upper limit on the length of a parallel data connection that is usually shorter than a serial connection. Complexity: Parallel data links are easily implemented in hardware, making them a logical choice. Creating a parallel port in a computer system is relatively simple, requiring only a latch to copy data onto a data bus.
Parallel ports send multiple bits at the same time over several sets of wires. Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-). After ports are connected, they typically require handshaking , where transfer type, transfer rate, and other necessary information is shared before data is sent.
Due to the lack of internal timing in the parallel ports, synchronization is implemented via software handshaking: four pins are used for data transfer and one is used for synchronization. The logical values at these pins are read and written directly by the software via an input or output instruction.
With the modes balance-rr, balance-xor, broadcast and 802.3ad, all physical ports in the link aggregation group must reside on the same logical switch, which, in most common scenarios, will leave a single point of failure when the physical switch to which all links are connected goes offline.
Parallel SCSI specifications include several synchronous transfer modes for the parallel cable, and an asynchronous mode. The asynchronous mode is a classic request/acknowledge protocol, which allows systems with a slow bus or simple systems to also use SCSI devices. Faster synchronous modes are used more frequently.
This is a list of TCP and UDP port numbers used by protocols for operation of network applications. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) only need one port for duplex, bidirectional traffic. They usually use port numbers that match the services of the corresponding TCP or UDP implementation, if they exist.